1. Field of the Invention
This invention relates to compositions including organosiloxane polymers containing sulfur and to a method of forming higher molecular weight products from such compositions. This invention also relates to organosiloxane gels, elastomers and resins containing sulfur.
2. Description of the Prior Art
Compositions containing mercaptoorganosiloxanes free of any vinyl functionality which are polymerized by means of the mercapto groups to resins and sealants are known in the art. For example, in U.S. Pat. No. 4,133,939, Bokerman and Gordon teach a method of coating a substrate with a silicone release coating involving the radiation cure of mercapto-functional polydiorganosiloxane fluids mixed with a sensitizer such as benzophenone. While a radiation curing mechanism is rapid and provides one-package systems stable in the absence of light and heat, it is useful only for relatively thin coatings and requires a high intensity radiation source such as ultraviolet light or electron beams.
Peroxide cure of mercaptoorganosiloxanes free of vinyl unsaturation is also known, as demonstrated by Homan and Lee in U.S. Pat. No. 4,070,329. In that patent, the patentees teach mixtures of mercaptoorganopolysiloxanes, organic peroxide and, optionally, a filler to provide a composition which cures at room temperature or by heating to form elastomers which are useful as sealants and rubber articles. Likewise, Homan and Lee in U.S. Pat. No. 4,070,328 claim mixtures of mercaptoorganopolysiloxanes, organic hydroperoxides, a nitrogen compound and, optionally, a filler which produce compositions which cure at room temperature to elastomers which are useful as sealants and rubber articles. However, the above compositions are not one-package systems since the polymerization or cure begins immediately upon mixing the ingredients.
Vanderlinde, in U.S. Pat. No. 3,445,419, teaches the production of a type of mercapto-functional copolymer consisting of organosiloxanes with mercapto-functional organic compound segments which are prepared by grafting a mercapto-functional carboxylic acid ester such as pentaerythritol tetrakis (3-mercapto-propionate) onto a vinyl-terminated organosiloxane. When an alkaline catalyst such as an amine is added to the resulting graft-copolymer, there is obtained a composition which is stable in the absence of air, but cures to an elastomer at room temperature upon exposure to air. However, to prepare the Vanderlinde compositions, the use of both an aliphatically unsaturated organopolysiloxane and a grafting operation which introduces an additional amount of organic compound into the cured product is required. Furthermore, Vanderlinde does not suggest that a cobaltocene can be used either to prepare or to polymerize or cure the compositions hereinafter described.